client: src: completion: fix for when Docker is not found

Per current default install instructions; as this is appended to either
the per-interactive-shell startup file or aliases file, if Docker is not
installed or is not found, without this fix, the end-user will either be
effectively locked out of their session (after logging out) or they will
not be able to start a new shell within their current session...

client/src/docker/completion.bash

@@ -30,7 +30,8 @@
 
 # If not yet installed, gracefully exit
 if ! hash docker &>/dev/null; then
-  exit 0
+  echo -e "\e[33;1m [WARN] Docker installation not found for docker-finance!\e[0m" >&2
+  return
 fi
 
 # TODO: HACK: needed for `plugins` completion